File generating method and file generating apparatus

ABSTRACT

A file generating method according to one aspect of the present disclosure is a file generating method for generating an MP4 file, the file generating method including: step S 11  of acquiring an original file made in a file format different from MP4; step S 12  of acquiring a difference file including data that is not included in the original file; step S 13  of acquiring a procedure file indicating a procedure for generating the MP4 file; and step S 14  of generating the MP4 file by combining the data included in the difference file and data included in the original file in accordance with the procedure indicated in the procedure file.

BACKGROUND

1. Technical Field

The present disclosure relates to a file generating method and filegenerating apparatus that generate MP4 files.

2. Description of the Related Art

A file format used for conventional optical discs is an MPEG2-TS (MPEG-2Transport Stream) scheme prescribed by ISO/IEC 138181-1. Hereinafter,the MPEG2-TS scheme is just referred to as MPEG2-TS. That is, a filemade through multiplexing of a video stream, voice stream, and subtitlestream in an MPEG2-TS file format is recorded in an optical disc.Specifically, according to MPEG2-TS, streams such as a video stream,voice stream, and subtitle stream are each divided into a plurality of188-byte TS packets, multiplexed, and recorded in an optical disc. ThisMPEG2-TS is optimized for broadcast or a medium like an optical discthat transmits or records data that is read and processed sequentiallyfrom top. Therefore, even a consumer electronic product with relativelysmall buffer capacity can read, decrypt, and play the streamefficiently.

In contrast, the file format currently used in content delivery over anetwork these days is the MP4 scheme prescribed by ISO/IEC 14496-12.Hereinafter, the MP4 scheme is just referred to as MP4. MP4 adoptsextremely flexible data structure on an assumption of application of MP4to a medium that allows random access, such as a HDD (Hard Disk Drive)and a flash memory. In a general usage pattern of this MP4, a streamsuch as a video stream, voice stream, and subtitle stream is dividedinto several-second units called fragment, and these fragments arearranged sequentially to constitute one file.

An optical disc is expected to be still utilized often as a medium fordistributing quality content, such as 4K, that is expected to be widelyused in the future, due to a problem of a price per bit. In contrast, asmart phone or tablet, which fails to have an optical disc drive, isused as a terminal for receiving and playing content distribution over anetwork, through utilization of high portability or recent large screenand high resolution. For this reason, a smart phone or tablet has a lotof functions and processing that conform to MP4, and application ofMPEG2-TS shows little progress.

Therefore, when content that is an MPEG2-TS file distributed with anoptical disc is copied to the smart phone or tablet, the file format ofthe content may be converted into MP4 (for example, refer to PatentLiterature 1). An MP4 file, which is a file of MP4, is generated by suchconversion.

CITATION LIST Patent Literature

-   PTL 1: Unexamined Japanese Patent Publication No. 2012-175608

SUMMARY OF THE INVENTION

In one general aspect, the techniques disclosed here feature a filegenerating method for generating an MP4 file, the file generating methodincluding: acquiring an original file made in a file format differentfrom MP4; acquiring a difference file including data that is notincluded in the original file; acquiring a procedure file indicating aprocedure for generating the MP4 file; and generating the MP4 file bycombining the data included in the difference file with data included inthe original file in accordance with the procedure indicated in theprocedure file.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically illustrating an example of contentstructure of MPEG2-TS stored in an optical disc;

FIG. 2 is a diagram for describing a decryption method of an AlignedUnit;

FIG. 3 is a diagram illustrating internal structure of the Aligned Unitin plain text;

FIG. 4 is a diagram illustrating a method for creating an actualElementary Stream from a plurality of TS Payloads;

FIG. 5 is a block diagram illustrating a configuration of a filegenerating apparatus according to an exemplary embodiment;

FIG. 6 is a diagram for describing a method for generating a stream fileof MP4 from a stream file of MPEG2-TS, difference file, and copymanifest file according to the exemplary embodiment;

FIG. 7 is a diagram for describing a method for generating a differencefile and copy manifest file according to the exemplary embodiment;

FIG. 8 is a flowchart of a file generating method according to theexemplary embodiment;

FIG. 9 is a diagram for describing the file generating method accordingto variation 1 of the exemplary embodiment;

FIG. 10A is a diagram for describing encryption of data in an AES-CTRmode according to variation 1 of the exemplary embodiment;

FIG. 10B is a diagram for describing decryption of data in the AES-CTRmode according to variation 1 of the exemplary embodiment;

FIG. 11 is a diagram illustrating an example of storing in an MP4 filean access unit of MPEG-4 AAC stored in a transport stream according tovariation 2 of the exemplary embodiment;

FIG. 12 is a diagram illustrating an example of storing in an MP4 filean access unit of MPEG-4 AVC stored in a transport stream according tovariation 2 of the exemplary embodiment;

FIG. 13A is a diagram illustrating an example of storage of an LATMheader and an LATM payload in a TS packet according to variation 2 ofthe exemplary embodiment;

FIG. 13B is a diagram illustrating an example of syntax of an AU_infotable according to variation 2 of the exemplary embodiment;

FIG. 13C is a diagram illustrating another examples of syntax of theAU_info table according to variation 2 of the exemplary embodiment;

FIG. 14 is a block diagram illustrating a configuration of the filegenerating apparatus according to variation 2 of the exemplaryembodiment;

FIG. 15A is a diagram illustrating schematic structure of an NAL unitaccording to variation 2 of the exemplary embodiment;

FIG. 15B is a diagram illustrating an example of a storage format of theNAL unit in MPEG2-TS according to variation 2 of the exemplaryembodiment;

FIG. 15C is a diagram illustrating an example of the storage format ofthe NAL unit in MP4 according to variation 2 of the exemplaryembodiment;

FIG. 16A is a diagram illustrating a configuration example of an accessunit in a transport stream according to variation 2 of the exemplaryembodiment;

FIG. 16B is a diagram illustrating an example of syntax of sizeinformation included in a size information NAL unit according tovariation 2 of the exemplary embodiment;

FIG. 16C is a diagram illustrating another example of syntax of the sizeinformation included in the size information NAL unit according tovariation 2 of the exemplary embodiment; and

FIG. 17 is a flowchart illustrating a processing operation that the filegenerating apparatus according to variation 2 of the exemplaryembodiment generates an MP4 file.

DETAILED DESCRIPTION Underlying Knowledge Forming Basis of the PresentDisclosure

The present inventors have found out that the following problems ariseregarding a file generating method of the above Patent Literature 1described in the column of “BACKGROUND ART”.

The file generating method of the above-described Patent Literature 1needs to temporarily restore content multiplexed by MPEG2-TS to eachstream, such as a video stream, voice stream, and subtitle stream, andthen to convert a file format of the content into MP4. Also, commercialcontent distributed with an optical disc is typically encrypted.Therefore, in conversion, it is necessary to decrypt the contenttemporarily, to convert the file format, and then to encrypt the contentagain. Hereinafter, structure of content of MPEG2-TS, etc. will bedescribed in detail.

FIG. 1 is a diagram schematically illustrating an example of contentstructure of MPEG2-TS stored in an optical disc. A Stream File is storedas content in the optical disc. Although only one Stream File is storedin the optical disc in the example illustrated in FIG. 1, a plurality ofStream Files may be stored. Also, the Stream File is recorded here witha file name of XXXXX.M2TS. A number is described in XXXXX. If aplurality of pieces of content is stored, it is possible to manage thosepieces of content individually with this number.

The Stream File is divided into a plurality of units, each of which is a6144-byte unit called Aligned Unit. The Aligned Unit is a unit ofencryption. Note that a data size of the Stream File may not necessarilybe a multiple of 6144 bytes. When the data size of the Stream File isnot a multiple of 6144 bytes, the data size of the Stream File ispreferably adjusted to a multiple of 6144 bytes by a method such asstoring NULL Data in a tail of the content.

FIG. 2 is a diagram for describing a decryption method of the AlignedUnit.

The content on the optical disc has been encrypted using a unit key Ku,which is data. In encryption, 6144-byte data included in the AlignedUnit is divided into 16-byte top data and remaining 6128-byte data, andthe remaining 6128-byte data is encrypted.

In decryption of the Aligned Unit, AES_E first encrypts 16-byte top datain accordance with an AES (Advanced Encryption Standard) encryptionscheme that uses the unit key Ku. Next, calculation of exclusive OR isperformed between data obtained by this encryption and the 16-byte topdata. AES_DCBC uses a result of this calculation of exclusive OR as akey to decrypt the remaining 6128-byte data in an AES-CBC (Cipher BlockChaining) mode. The 16-byte top data is added to data in plain textobtained by this decryption. As a result, 6144-byte plain textcorresponding to the Aligned Unit is obtained.

FIG. 3 is a diagram illustrating internal structure of the Aligned Unitin plain text.

The Aligned Unit includes 32 Source Packets, each of which has 192bytes. Each Source Packet includes a TP_extra_header, which is a 4-byteheader, and a 188-byte Transport Packet, which is a TS packet.Furthermore, the 188-byte Transport Packet includes a 4-byte TS Headerand a 184-byte TS Payload. The TS Header describes information thatindicates an attribute of the TS Payload. Specifically, the TS Headerincludes sync_byte (8 bits), transport_error_indicator (1 bit),payload_unit_start_indicator (1 bit), transport_priority (1 bit), PID(13 bits), transport_scrambling_control (2 bits),adaptation_field_control (2 bits), and continuity_counter (4 bits).Here, PID is information for identifying a type of an elementary streamstored in the TS Payload, for example, video or voice. Also, even whenthere is a plurality of voice types, the voice type of the elementarystream can be identified by this PID.

FIG. 4 is a diagram illustrating a method for creating an actualElementary Stream from a plurality of TS Payloads. A PES_Header and theElementary Stream are made through connection of the plurality of TSPayloads to which identical PID is allocated. Here, the first TS Payloadof the plurality of TS Payloads is formed to include the PES_Header.Note that a PES (Packetized Elementary Stream) or a PES packet is formedfrom the PES_Header and at least part of the Elementary Stream.

As described above, the MPEG2-TS file (Sterem File) is encrypted foreach Aligned Unit. Therefore, in order to convert the file into an MP4file, the above-described decryption is performed, and re-encryption isfurther performed. A conversion device, such as a smart phone or atablet, has a problem that such decryption and encryption take time.Furthermore, since content in plain text is created temporarily, thereis also a problem from a security viewpoint.

To solve such problems, a file generating method according to one aspectof the present disclosure is a file generating method for generating anMP4 file, the file generating method including: acquiring an originalfile made in a file format different from MP4; acquiring a differencefile including data that is not included in the original file; acquiringa procedure file indicating a procedure for generating the MP4 file; andgenerating the MP4 file by combining the data included in the differencefile with data included in the original file in accordance with theprocedure indicated in the procedure file. For example, in acquisitionof the original file, the original file made in a file format ofMPEG2-TS is acquired.

This causes the MP4 file to be generated through combination of the dataincluded in the difference file and the data included in the originalfile in accordance with the predetermined procedure. Therefore, thisallows the MP4 file to be easily generated without restoring theoriginal file formed in the file format such as MPEG2-TS to each streamsuch as a video stream and a voice stream. In addition, even if theoriginal file is encrypted, it is not necessary to decrypt andre-encrypt the original file. Therefore, a processing load forgenerating the MP4 file may be reduced.

In addition, the original file, the difference file, and the procedurefile may be acquired through reading of the original file, thedifference file, and the procedure file, respectively, from an opticaldisc.

This allows all the files required for generation of the MP4 file to beacquired from one optical disc, and thus saves time and effort forsearching for those files, and allows the MP4 file to be generated moreeasily.

Also, the procedure file may describe ranges of a plurality ofrespective sections included in the difference file, and ranges of aplurality of respective sections included in the original file, so thatthe ranges of the sections included in the difference file and theranges of the sections included in the original file may be arrangedalternately. In generation of the MP4 file, the MP4 file may begenerated through combination of the sections indicated by therespective ranges in order of the respective ranges described in theprocedure file.

This allows each section included in the MP4 file to be generated inorder from top of the MP4 file, and since generation processing does notgo backward, the MP4 file can be generated more easily.

Also, the ranges of the plurality of respective sections included in thedifference file may be described in the procedure file in data size. Theranges of the plurality of respective sections included in the originalfile may be described in the procedure file in starting position anddata size of the sections.

This allows appropriate sections to be copied or acquired from thedifference file and the original file, and to be combined in accordancewith description in the procedure file. Also, since the startingposition is not used for description of the range of the sectionincluded in the difference file, the data size of the procedure file maybe reduced.

Also, the data size of the MP4 file may be described in the procedurefile. The file generating method may further determine whether a mediumhas free space for recording the MP4 file based on the data size of theMP4 file described in the procedure file.

Since this determines whether the medium has free space for recordingthe MP4 file, if the medium does not have enough free space, processingsuch as stopping generation of the MP4 file in advance can be performed.That is, occurrence of errors can be prevented.

In addition, an attribute of the MP4 file may be described in theprocedure file, and the file generating method may further read theattribute described in the procedure file.

The allows previous determination to be made whether the desired MP4file will be generated if the attribute of the MP4 file is read from theprocedure file before generation of the MP4 file.

Also, a buffer size required for playback of the MP4 file may bedescribed in the procedure file, and the file generating method mayfurther read the buffer size described in the procedure file.

This allows determination to be made easily whether the MP4 file can beplayed without analysis of the MP4 file if the buffer size required forplayback of the MP4 file is read from the procedure file.

Also, a first file name, which is a name of the original file, and asecond file name, which is a name of the difference file, may bedescribed in the procedure file. The file generating method may furtherspecify a file with the first file name described in the procedure fileas the original file, and may specify a file with the second file namedescribed in the procedure file as the difference file.

This allows appropriate acquisition of the original file and differencefile to be used for generation of the MP4 file.

Also, in generation of the MP4 file, MP4-conforming header informationthat is data included in the difference file may be combined with dataincluded in the original file.

This allows the MP4 file that has appropriate header information of MP4to be easily generated.

Also, in acquisition of the original file, the original file in plaintext may be acquired, and in generation of the MP4 file, the generatedMP4 file may be encrypted.

This allows confidentiality of data included in the original file to besecured while the data is left as the MP4 file, if the original file isdeleted after conversion to MP4.

Also, in generation of the MP4 file, every time a section thatconstitutes the original file is acquired, a portion of the MP4 filecorresponding to the section may be generated and encrypted. Every timethe portion that constitutes the MP4 file is encrypted, the section ofthe original file corresponding to the portion may be deleted.

This makes it possible to prevent all data included in the original filein plain text from being stored even temporarily in a storage area, andallows confidentiality of the data to be secured more certainly.

Hereinafter, an exemplary embodiment will be specifically described withreference to the drawings.

Note that all exemplary embodiment to be described below illustratescomprehensive or specific examples. Numerical values, shapes, materials,components, arrangement positions and connection forms of thecomponents, steps, order of the steps, and the like indicated in thefollowing exemplary embodiment are one example, and do not intend tolimit the present disclosure. Also, among the components described inthe following exemplary embodiment, components that are not described inan independent claim which represents the highest concept are describedas optional components.

Exemplary Embodiment

FIG. 5 is a block diagram illustrating a configuration of a filegenerating apparatus according to the present exemplary embodiment.

File generating apparatus 10 according to the present exemplaryembodiment is an apparatus that generates an MP4 file, and includesoriginal file acquisition unit 11, difference file acquisition unit 12,procedure file acquisition unit 13, and generation unit 14. Originalfile acquisition unit 11 acquires an original file that is made in afile format different from MP4. Difference file acquisition unit 12acquires a difference file including data that is not included in theoriginal file. Procedure file acquisition unit 13 acquires a procedurefile that indicates a procedure for generating the MP4 file. Generationunit 14 generates the MP4 file through combination of the data includedin the difference file and data included in the original file inaccordance with the procedure indicated in the procedure file. In otherwords, generation unit 14 converts the original file into the MP4 file.

Hereinafter, a processing operation performed by this file generatingapparatus 10 will be described in detail.

FIG. 6 is a diagram for describing a method for generating a stream fileof MP4 from a stream file of MPEG2-TS, a difference file, and a copymanifest file.

According to the present exemplary embodiment, a stream file A(XXXXX.M2TS), which is the above original file, a copy manifest file(XXXXX.CMNF), which is the above procedure file, and the abovedifference file (XXXXX.DMP4) are recorded, for example, in an opticaldisc (for example, Blu-ray (registered trademark) disc). The copymanifest file (XXXXX.CMNF) describes a conversion procedure about how toprocess and convert this original file into the MP4 file. The differencefile (XXXXX.DMP4) stores data required for conversion into the MP4 file.

When converting the stream file A of MPEG2-TS (XXXXX.M2TS), generationunit 14 alternately combines data of the stream file A (XXXXX.M2TS) anddata of the difference file (XXXXX.DMP4) in accordance with descriptionof the copy manifest file (XXXXX.CMNF) to generate a stream file B (XXXXX.MP4), which is the MP4 file. In other words, generation unit 14converts the stream file A (XXXXX.M2TS) into the stream file B(XXXXX.MP4).

This allows conversion of the original file without restoring theoriginal file to an elementary stream of voice or video (for example,stream of HE-AAC or MPEG-4 AVC). Also, when the original file has beenencrypted, the original file may be converted into the MP4 file easilywithout decryption.

This copy manifest file (XXXXX.CMNF) includes “Input File A”, “InputFile B”, “Output File”, “Output File Size”, “ATTRIBUTE”, “MP4 DECODERBUFFER SIZE”, and “COPY MANIFEST”. “Input File A” and “Input File B”respectively denote file names of two files to be input. Conversionprocessing starts with copy of a top section of the file denoted by“Input File A”. “Output File” denotes a file to be output, that is, afile name of the MP4 file to be generated. “Output File Size” denotes adata size of the MP4 file to be output. This data size is described to aprecision of one byte. Checking this data size allows confirmationbefore conversion processing whether a medium that records the MP4 fileto be output has sufficient free space. “ATTRIBUTE” denotes an attributeof each file, and specifically denotes what kind of elementary stream isconverted and what kind of file is generated. In the example illustratedin FIG. 6, “ATTRIBUTE” denotes that the MP4 file after conversionincludes a 4K video compressed by HEVC (High Efficiency Video Coding),and 5.1 ch English voice of AAC (Advanced Audio Coding). This allowsprevious confirmation before conversion processing what kind of filewill be obtained after conversion when the file is converted inaccordance with this copy manifest file. Also, “ATTRIBUTE” may denoteinformation such as data structure of the MP4 file, and may denote abrand (that is, a type) of MP4 to be stored in “ftyp” of the MP4 file.

Also, “MP4 DECODER BUFFER SIZE” denotes a buffer size that is a minimumrequirement for playing the stream file B after conversion (XXXXX.MP4),which is the MP4 file to be output. This buffer size is an amountdepending on under what kind of multiplexing rule a video, voice, etc.are multiplexed in the MP4 file, which is the stream file B afterconversion. “MP4 DECODER BUFFER SIZE” may denote what kind of decoderresource (memory capacity and data transfer rate) is required forplaying the stream file B after conversion, in addition to the buffersize.

“COPY MANIFEST” denotes a range of each section of the file denoted by“Input File A” and a range of each section of the file denoted by “InputFile B”. Each of these sections is a section that is sequentially copiedand pasted for generating the MP4 file denoted by “Output File”. Also,the range of each section is denoted by a copy starting position and acopy size, or by only the copy size. Also, in order to cause the sectionof the file denoted by “Input File A” and the section of the filedenoted by “Input File B” to be copied and pasted repeatedly andalternately, “COPY MANIFEST” denotes the range of each section of thosefiles.

Each section of the specified size of the difference file (XXXXX.DMP4)is copied and pasted from top of the difference file. Therefore, “COPYMANIFEST” does not need to specify the copy starting position toindicate each section of the difference file (XXXXX.DMP4). That is, therange of each section of the difference file is indicated by only thecopy size (data size) without using the copy starting position.

On the other hand, the stream file A (XXXXX.M2TS) includes dataunnecessary for the stream file B after conversion (XXXXX.MP4).Therefore, in order to indicate each section of the stream file A thatis the original file, “COPY MANIFEST” indicates the range of eachsection with the copy starting position and the copy size. The copystarting position is a byte position from top of the file, and the copysize is a data size in byte unit.

Generation unit 14 repeats an alternate copy and paste of a sectionincluded in the original file and a section included in the differencefile indicated by “COPY MANIFEST”, in accordance with the copy manifestfile. That is, generation unit 14 repeats alternate combination of thesection included in the original file and the section included in thedifference file, indicated by “COPY MANIFEST”. Accordingly, the MP4 filethat is the stream file B after conversion is generated.

Therefore, in accordance with the copy manifest file, conversion of theoriginal file performed by any device enables generation of theidentical stream file B after conversion (XXXXX.MP4). That is, thisfacilitates playback of the stream file B after conversion by any devicewithout any problem.

Note that file generating apparatus 10 may acquire the difference file(XXXXX.DMP4) and the copy manifest file (XXXXX.CMNF) from an opticaldisc, such as a Blu-ray (registered trademark) disc, and may acquireboth of or one of these files via the Internet. In this case, it ispossible to present various options to a user, such as converting theoriginal file into a file in the latest file format or into an MP4 fileincluding another video and voice, without any special change requiredin file generating apparatus 10.

Also, file generating apparatus 10 may perform conversion with thestream file A, which is the original file, being encrypted, or mayperform conversion into the MP4 file after decryption of the originalfile, and encrypt the generated MP4 file again. Also, the file stream(XXXX X.M2TS), which is the original file, may be plain text. Note thatsince the difference file includes header information, encryption of thedifference file is unnecessary. However, when the stream file A(XXXXX.M2TS), which is the original file, or the stream file B(XXXXX.MP4), which is the MP4 file, is plain text, an operation ofdeveloping the entire file in a memory, or retaining the entire filetemporarily in a hard disk may not be allowed from a security viewpoint.

Therefore, in order from a region in which conversion to the MP4 filehas finished, file generating apparatus 10 may delete the region, out ofthe stream file A (XXXXX.M2TS), which is the original file in plaintext. Also, when encrypting the stream file B (XXXXXX.MP4), which is theMP4 file, every time “Movie fragment” included in the MP4 file or asection such as a predetermined number of MP4 samples is generated, filegenerating apparatus 10 may encrypt the generated section sequentially.Note that when an encryption scheme is used under which the data sizedoes not change before and after the encryption, the data region to becopied does not change regardless of whether the data is encrypted.

Also, the copy manifest file may indicate whether the stream file A(XXXXX.M2TS), which is the original file, has been encrypted.Alternatively, the copy manifest file may indicate whether to convertthe stream file A with the multiplexed coded data being encrypted, orwhether to decrypt the encrypted coded data into plain text, to convertthe data into an MP4 file, and then to encrypt the MP4 file again.

FIG. 7 is a diagram for describing a method for generating thedifference file and the copy manifest file.

The difference file (XXXXX.DMP4) and the copy manifest file (XXXXX.CMNF)may be generated as follows. In an authoring stage, format conversion isperformed on the stream file A (XXXXX.M2TS), which is the original file,to generate the stream file B after conversion (XXXXX.MP4), which is theMP4 file. Next, at least one section is searched for, including datathat coincides with each other between the stream file A, which is theoriginal file, and the stream file B. At this time, the search isperformed so that the data size of each section may be maximized. Next,the difference file is generated by connecting each of the remainingsections other than the section searched for as described above includedin the stream file B in order included in the stream file B. Acorrelation result of each file at this time is recorded in the copymanifest file as “COPY MANIFEST”.

Note that the above-described search is performed through sequentialacquisition of data included in each of the stream file A and the streamfile B in a backward direction from top of each file, and throughcomparison of those pieces of data. This comparison is performed withoutreturning in a direction opposite to the above-described direction. Thisallows the above-described conversion processing (copy processing) to beperformed sequentially, that is by one continuous process, and allowsachievement of high speed or small memory.

Note that when a video and audio are multiplexed by MPEG2-TS, in orderto prevent underflow of data of a picture with a large amount of codes,such as I picture, a picture of predetermined PTS (Presentation TimeStamp) included in the video may be multiplexed earlier in time,compared with a frame of PTS identical to the predetermined PTS includedin audio. On the other hand, when a video and audio are multiplexed byMP4, it is common that the multiplexing is performed so that PTS of thetop picture of the video and PTS of the top frame of the audio in “Moviefragment” may coincide with each other or may be in proximity.

Thus, if a multiplexing unit of audio, video, or text differs betweenthe stream file A and the stream file B, conversion processing may notbe performed sequentially. As a result, conversion may be performedwhile a pointer for reading or writing is moved forward and backwardsequentially. Therefore, information such as whether conversionprocessing may be performed by one continuous process, and a maximumdata size for required backtracking when conversion processing cannot beperformed by one continuous process may be registered in the copymanifest file.

Note that if a search to be performed of the stream file A and thestream file B for a section including coincident data is performed in asmall unit of data, the data size of the copy manifest file becomeslarge, or conversion processing becomes complicated. For this reason, aspecific threshold may be provided. For example, only a sectionincluding data of which eight bytes or more coincide with each other isregistered in the copy manifest file. Even if each of the remainingsections other than the above section included in the stream file Bincludes data that coincides with data of the stream file A, the databeing shorter than 8 bytes, the data included in those remainingsections is stored in the difference file. Also, this threshold may bedescribed as “MIN COPY SIZE: 8 bytes” in the copy manifest file.

Also, a file of MPEG-2 TS may be converted into an MP4 file by using thecopy manifest file that indicates a multiplexing unit in the MP4 file,without using the difference file. In MP4, for example, audio, video,and text are multiplexed as “Movie fragment” that differs from oneanother. At this time, information such as DTS of each of an audio frameand video picture that are top and end of “Movie fragment” in order ofdecryption, and a byte offset value from top of a file of MPEG-2 TS maybe registered together with identification information about the medium.It is assumed here that order of registration of “Movie fragment”coincides with order of appearance of “Movie fragment” in the MP4 file.

FIG. 8 is a flowchart of a file generating method according to thepresent exemplary embodiment.

The file generating method according to the present exemplary embodimentis a method by which file generating apparatus 10 generates the MP4file. In this file generating method, first, original file acquisitionunit 11 of file generating apparatus 10 acquires the original file thatis made in the file format different from MP4 (step S11). Next,difference file acquisition unit 12 acquires the difference fileincluding data that is not included in the original file (step S12).Next, procedure file acquisition unit 13 acquires the procedure filethat indicates the procedure for generating the MP4 file (step S13).Then, in accordance with the procedure indicated in the procedure file,generation unit 14 combines the data included in the difference file anddata included in the original file to generate the above-described MP4file (step S14). For example, in step S11, original file acquisitionunit 11 acquires the original file that is made in the file format ofMPEG2-TS.

Accordingly, in accordance with the predetermined procedure, the MP4file is generated through combination of the data included in thedifference file and the data included in the original file. Therefore,the MP4 file can be easily generated without restoring the original filemade in the file format such as MPEG2-TS to each stream such as thevideo stream and the voice stream. Also, even if the original file hasbeen encrypted, it is not necessary to decrypt and re-encrypt theoriginal file. Therefore, a processing load for generating the MP4 filemay be reduced.

Also, in steps S11 to S13, original file acquisition unit 11, differencefile acquisition unit 12, and procedure file acquisition unit 13 readthe original file, difference file, and procedure file from the opticaldisc, respectively, to acquire those files. This allows all the filesrequired for generation of the MP4 file to be acquired from one opticaldisc, and thus saves time and effort for searching for those files, andallows the MP4 file to be generated more easily.

Here, the procedure file describes ranges of a plurality of respectivesections included in the difference file, and ranges of a plurality ofrespective sections included in the original file, so that the ranges ofthe sections included in the difference file and the ranges of thesections included in the original file may be arranged alternately.Therefore, in step S14, generation unit 14 combines the sectionsindicated by the respective ranges in order of the respective rangesdescribed in the procedure file to generate the MP4 file. This allowseach section included in the MP4 file to be generated in order from topof the MP4 file, and since the processing does not go backward, the MP4file can be generated more easily.

Also, the ranges of the plurality of respective sections included in thedifference file are described in the procedure file in data size. On theother hand, the ranges of the plurality of respective sections includedin the original file are described in the procedure file in startingposition and data size of the section. This allows appropriate sectionsto be copied or acquired from the difference file and the original file,and to be combined in accordance with description in the procedure file.Also, since the starting position is not used for description of therange of the section included in the difference file, the data size ofthe procedure file may be reduced.

Also, the data size of the MP4 file is described in the procedure file.Therefore, in step S14, generation unit 14 may further determine whetherthe medium has free space for recording the MP4 file based on the datasize of the MP4 file described in the procedure file. Since thisdetermines whether the medium has free space for recording the MP4 file,if the medium does not have enough free space, processing such asstopping generation of the MP4 file in advance can be performed. Thatis, occurrence of errors can be prevented.

Also, the attribute of the MP4 file is described in the procedure file.Therefore, file generating apparatus 10 may further read the attributedescribed in the procedure file.

This allows previous determination to be made whether the desired MP4file will be generated, if the attribute of the MP4 file is read fromthe procedure file before generation of the MP4 file.

Also, the buffer size required for playback of the MP4 file is describedin the procedure file. Therefore, file generating apparatus 10 mayfurther read the buffer size described in the procedure file. Thisallows determination to be made easily whether the MP4 file can beplayed without analysis of the MP4 file, if the buffer size required forplayback of the MP4 file is read from the procedure file.

Also, a first file name, which is a name of the original file, and asecond file name, which is a name of the difference file, are describedin the procedure file. Therefore, file generating apparatus 10 mayfurther specify a file with the first file name described in theprocedure file as the original file, and may specify a file with thesecond file name described in the procedure file as the difference file.This allows appropriate acquisition of the original file and differencefile to be used for generation of the MP4 file.

Also, in step S14, generation unit 14 combines MP4-conforming headerinformation that is data included in the difference file with dataincluded in the original file. This allows the MP4 file that hasappropriate header information of MP4 to be easily generated.

Also, in step S11, original file acquisition unit 11 may acquire theoriginal file in plain text, and in step S14, generation unit 14 mayencrypt the generated MP4 file. This allows confidentiality of dataincluded in the original file to be secured while leaving the data asthe MP4 file, if the original file is deleted after conversion to MP4.

Here, in step S14, every time a section that constitutes the originalfile is acquired, generation unit 14 may generate and encrypt a portionof the MP4 file corresponding to the section, and every time the portionthat constitutes the MP4 file is encrypted, generation unit 14 maydelete the section of the original file corresponding to the portion.This makes it possible to prevent all data included in the original filein plain text from being stored even temporarily in a storage area, andallows confidentiality of the data to be secured more certainly.

Variation 1

Although the above-described exemplary embodiment uses the differencefile and the copy manifest file to generate the MP4 file, the MP4 filemay be generated without using these files. In a file generating methodaccording to the present variation, a counter is used to convert astream file of MPEG2-TS made of a plurality of Source Packets, each ofwhich has a header in plain text, into a stream file of MP4. This causesthe stream file of MP4 to be generated. Note that the stream file ofMPEG2-TS is the original file, and the stream file of MP4 is the MP4file.

FIG. 9 is a diagram for describing the file generating method accordingto the present variation.

The stream file (that is, content) of MPEG2-TS includes the plurality ofSource Packets, as described above. Note that each of the Source Packetsis abbreviated as SP in FIG. 9.

In each Source Packet included in the stream file of MPEG2-TS in thepresent variation, only a TS Payload section of data included in theSource Packet is encrypted. That is, of the data included in the SourcePacket, TS_extra_header and TS Header are not encrypted but are plaintext.

An AES-CTR (CounTeR) mode is used for encryption. Note that in theAES-CTR mode, encryption and decryption using a value of the counter areperformed. As illustrated in FIG. 9, the value of the counter for video(AES Counter for Video) is used to encrypt the plurality of TS Payloadseach including data of video. The value of the counter for audio (AESCounter for Audio) is used to encrypt the plurality of TS Payloads eachincluding data of audio. The counter for video counts only data of theSource Packet of video so that the count value may increase inaccordance with an arrow illustrated in FIG. 9. The counter for audiocounts only data of the Source Packet of audio so that the count valuemay increase in accordance with an arrow illustrated in FIG. 9. Notethat details of encryption in the AES-CTR mode will be described later.

A file generating apparatus can convert the stream file of MPEG2-TS intothe stream file of MP4 easily by extracting only the TS Payload fromeach of the plurality of Source Packets included in the stream file ofMPEG2-TS.

FIG. 10A is a diagram for describing encryption of data by the AES-CTRmode.

In encryption, a key and IV (Initial Vector), which is an initial value,are used. First, the key is used to encrypt IV. Calculation of exclusiveOR between this value resulting from encryption and top 16 bytes of datato be encrypted (m1 illustrated in FIG. 10A) generates ciphertext c1corresponding to the top 16 bytes. Data (block) of next 16 bytes (m2illustrated in FIG. 10A) included in the data to be encrypted undergoesprocessing identical to the above-mentioned processing performed on thetop 16 bytes after IV is updated, like IV=IV+1. This causes ciphertextc2 corresponding to the next 16-byte data to be generated. The IVupdated as described above is the above counter value. The counter forvideo and the counter for audio illustrated in FIG. 9 each calculateIV=IV+1.

Performing such processing continuously allows the ciphertext to becreated even for long data of 16 bytes or more. Note that when a lengthof the data to be encrypted is not a multiple of 16 bytes, performingexclusive OR on a bit-by-bit basis in a tail block generates theciphertext.

FIG. 10B is a diagram for describing decryption of data by the AES-CTRmode.

In decryption, processing completely identical to processing ofencryption is performed on data to be decrypted. That is, processing forencrypting IV by using the key is performed also in decryption.

Thus, the file generating method according to the present variation is afile generating method for generating the MP4 file. The file generatingmethod acquires the original file made of a plurality of packets,acquires only a remaining encrypted payload section of the packetexcluding header information in plain text for each packet included inthe original file, and generates the MP4 file through combination of thepayload section. For example, in acquisition of the original file, theoriginal file made in the file format of MPEG2-TS is acquired. Thisallows the MP4 file to be easily generated, without restoring theoriginal file formed in a file format such as MPEG2-TS to each streamsuch as a video stream and a voice stream. Also, it is not necessary todecrypt and re-encrypt the original file. Therefore, a processing loadfor generating the MP4 file may be reduced.

Here, among the plurality of packets included in the original file, thepayload of each of the plurality of packets including data of video isencrypted using a counter value of a first counter for video. Thepayload of each of the plurality of packets including data of audio isencrypted using a counter value of a second counter for audio differentfrom the first counter. The first counter counts only data included ineach of the plurality of packets corresponding to video, backward fromtop of the original file. The second counter counts only data includedin each of the plurality of packets corresponding to audio, backwardfrom top of the original file. Accordingly, since the first counter isused as a counter dedicated to video, in the MP4 file, it is possible toeasily decrypt a video elementary that is formed through combination ofthe payload of each of the plurality of packets corresponding to video.Similarly, since the second counter is used as a counter dedicated toaudio, in the MP4 file, it is possible to easily decrypt an audioelementary that is formed through combination of the payload of each ofthe plurality of packets corresponding to audio.

Note that the original file includes a plurality of Aligned Units, andeach of the plurality of Aligned Units includes the plurality of SourcePackets. The plurality of packets included in the original file is theplurality of Source Packets included in each of the plurality of AlignedUnits. Also, the payload is the TS Payload, and the header informationis made of TP_extra_header and TS Header.

Variation 2

Although the above-described exemplary embodiment uses the differencefile and the copy manifest file to generate the MP4 file, the MP4 filemay be generated without using these files. A file generating methodaccording to the present variation converts the stream file of MPEG2-TSincluding supplementary information into the stream file of MP4 by usingthe supplementary information. This causes the stream file of MP4 to begenerated.

Since part of a data multiplexing method of an access unit differsbetween MPEG2-TS and MP4, when storing data of MPEG2-TS in the MP4 file,it is necessary to separate the access unit into a plurality of sectionsand to store those sections separately. Basically, the access unit inMPEG2-TS includes both initialization information required fordecryption of a picture of video or a frame of audio, and coded data ofa picture or a frame. On the other hand, the access unit in the MP4 file(referred to as a sample or MP4 sample in MP4) includes only coded dataof a picture or a frame. The initialization information required fordecryption is stored separately from the coded data as headerinformation of the MP4 file.

Hereinafter, description will be provided about supplementaryinformation for reducing an amount of processing required for conversionof the coded data multiplexed by MPEG2-TS into an MP4 file, and about aconversion method of a multiplexed format by using the supplementaryinformation. In particular, when the coded data is encrypted, an amountof processing for decryption and re-encryption is large. The presentvariation enables conversion to an MP4 file only by copy of data,without decryption of the coded data.

Note that the stream file of MPEG2-TS, which is the original file beforeconversion, may be another TS (transport stream). That is, the originalfile is not only TS specified by an MPEG-2 system, but also may be TSobtained by appending header information with a predetermined number ofbytes to a TS packet (for example, TS used in a Blu-ray (registeredtrademark) disc or video distribution). Also, the MP4 file generated byconversion may be an MP4 file that uses “Movie fragment”, and may be anMP4 file that does not use “Movie fragment”. Furthermore, the format ofthe file generated by conversion may be a format such as CFF (CommonFile Format) of DECE (Digital Entertainment Content Ecosystem) extendedbased on MP4, or MPEG-DASH (Dynamic Adaptive Streaming over HTTP). Thefollowing description assumes that the original file is the transportstream.

FIG. 11 is a diagram illustrating an example of storing in the MP4 filethe access unit of MPEG-4 AAC stored in the transport stream.

The access unit of MPEG-4 AAC in the transport stream includes threetypes of data: LATM (Low Overhead Audio Transport Multiplex) header,PayloadLengthInfo( ), and PayloadMux( ). The LATM header includesinitialization information required for decryption of coded data ofMPEG-4 AAC, such as a number of channels and a sampling frequency (alsoreferred to as AAC data). More particularly, the initializationinformation is stored in AudioSpecificConfig( ) in the LATM header. Asize of PayloadMux( ) is stored in PayloadLengthInfo( ), and AAC data isstored in PayloadMux( ).

When the data of the access unit is stored in the MP4 file,AudioSpecificConfig( ) in the LATM header is stored in a sample entry instsd within moov of the MP4 file. Furthermore, PayloadLengthInfo( ) andPayloadMux( ) are stored in mdat as sample data. Note that the sampledata is data to be stored in the sample. Also, the sample data withinmdat is referred to from moov, or, when “Movie fragment” is used, thesample data within mdat is referred to from moof. In MPEG-2 AAC, not theLATM header but an ADTS (Audio Data Transport Stream) header is used,and the access unit includes the ADTS header and AAC data (referred toas raw_data_block( ). Also at this time, the ADTS header is separatedfrom the access unit, and at least adts_fixed_header( ) of data includedin the ADTS header is stored in the sample entry. Furthermore, the AACdata is stored in mdat as sample data.

FIG. 12 is a diagram illustrating an example of storing in MP4 theaccess unit of MPEG-4 AVC (Advanced Video Coding) stored in thetransport stream.

As is the case with MPEG-4 AAC, in the transport stream, initializationinformation required for decryption, such as Sequence Parameter Set(SPS) and Picture Parameter Set (PPS), is stored as part of the accessunit. On the other hand, in the MP4 file, these pieces of initializationinformation are stored as header information of the MP4 file. The accessunit illustrated in FIG. 12 constitutes an IDR (Instantaneous DecoderRefresh) picture. An NAL (Network Adaptation Layer) unit of each of SPSand PPS is separated from the access unit and is stored in the sampleentry in stsd within moov of the MP4 file. Other data included in theaccess unit is stored in mdat as sample data.

Note that in MP4, a mode that allows the sample data of MPEG-4 AVC toinclude the initialization information such as SPS and PPS can beselected. The mode is indicated by the identification information on thesample entry. When the identification information is “avc1” or “avc2”,it is prohibited to include the initialization information in the sampledata. On the other hand, when the identification information is “avc3”or “avc4”, it is allowed to include the initialization information inthe sample data. Therefore, in conversion of the transport stream intothe MP4 file, when the above-described identification information in theMP4 file is set to “avc1” or “avc2”, the NAL unit of SPS and PPS, or theNAL unit of FillerData used for stuffing is deleted from the data storedin mdat from the access unit in the transport stream. Also, when theidentification information is set to “avc3” or “avc4”, it is notnecessary to delete the NAL unit of SPS or PPS. Therefore, whether todelete SPS and PPS may be switched in accordance with a setting value ofthe identification information in the MP4 file.

Also, data of HEVC (High Efficiency Video Coding), which is anext-generation video coding scheme, is made of the NAL unit in asimilar manner to MPEG-4 AVC, and includes the initializationinformation such as SPS and PPS. When the data of HEVC is stored in theMP4 file, the initialization information may be included in the sampledata. Therefore, when the transport stream is converted into the MP4file, of data to be stored in mdat from the access unit in the transportstream, whether to delete the initialization information may bedetermined in accordance with a type of the coding scheme, andprocessing may be performed in accordance with a result of thedetermination.

As described above, when the coded data of MPEG-4 AAC is stored in theMP4 file, the LATM header is separated from the access unit.Furthermore, only PayloadLengthInfo( ) and PayloadMux( ) are stored inmdat as sample data. Hereinafter, PayloadLengthInfo( ) and PayloadMux( )are together referred to as LATM payload.

Therefore, in the present variation, when data of the access unit ofMPEG-4 AAC is stored in the plurality of TS packets, the LATM header andLATM payload are stored in separate TS packets. This allows the LATMheader to be easily separated.

FIG. 13A is a diagram illustrating an example of storage of the LATMheader and the LATM payload in the TS packet. Stuffing is performed asnecessary so that data of the LATM header and data of the LATM payloadmay not be intermingled within the payload of the identical TS packet.For example, the LATM header of access unit 1 is stored in the payloadof the top TS packet. At this time, when the size of the LATM header isless than the size of the TS payload, stuffing is performed to aremaining region of the TS payload. Note that, although the PES packetis not described in the example illustrated in FIG. 13A, actually, dataof the access unit is stored in the payload of the PES packet, and dataof the PES packet is stored in the payload of the TS packet.

Next, a method will be described for identifying the TS packet in whichthe LATM header is stored and the TS packet in which the LATM payload isstored. When one access unit is stored as one PES packet,payload_unit_start_indicator of the TS header is set to 1 in the TSpacket including the top data of the PES packet. If it is guaranteedthat the LATM header is included in the payload of the TS packet inwhich payload_unit_start_indicator is set to 1, it is possible todetermine whether the LATM header is included within the TS packet,based on a value of payload_unit_start_indicator. When a plurality ofaccess units is stored in one PES packet, the AU_info table, which issupplementary information, may be arranged at top of the payload of thePES packet. This AU_info table includes a number of access unitsincluded in the payload of the PES packet, and sizes of the LATM headerand the LATM payload in each access unit.

FIG. 13B is a diagram illustrating an example of syntax of the AU_infotable.

The AU_info table includes AU_info_identification_code, number of AUthat denotes the number of access units, and size_of LengthInfo thatdenotes the sizes of the LATM header and the LATM payload in the accessunit. AU_info_identification_code is a bit string unique to the AU_infotable. It is possible to determine whether the AU_info table exists bysearching for this code. Alternatively, as in Box structure of MP4, theAU_info table may have data structure that combines a data size of Boxwith a type of Box. However, when existence of the AU_info table issignaled by information such as a descriptor in the transport stream, orsupplementary data for conversion to the MP4 file prepared separatelyfrom the transport stream, the code described above may be omitted.Also, when one access unit is stored in one PES packet, the AU_infotable may be used.

By indicating such size or data offset of each component in the accessunit, a technique for specifying data to be separated for conversion tothe MP4 file may be applied to coded data of MPEG-4 AVC. That is, whenthe coded data of MPEG-4 AVC is stored in the MP4 file, the techniquedescribed above may be applied in order to separate the NAL unit of eachof SPS and PPS.

FIG. 13C is a diagram illustrating an example of syntax of the AU_infotable for indicating whether it is necessary to exclude a component fromsample data of the MP4 file for each component in the access unit.

The AU_info table includes AU_info_identification_code,number_of_data_unit, size_of_data_unit, and conversion_mode.number_of_data_unit denotes a number of data units included in theaccess unit. size_of_data_unit denotes a size of the data unit.conversion_mode is a conversion mode that indicates how to handle thedata unit at a time of conversion to the MP4 file. If conversion_mode is0, the conversion_mode indicates to copy the data unit as sample data ofthe MP4 file. Also, if conversion_mode is 1, the conversion_modeindicates to exclude the data unit from the sample data, that is, not tocopy the data unit as the sample data.

Note that when conversion_mode is 1, the conversion_mode may indicatehandling of the data unit after excluding the data unit. For example,the conversion_mode indicates information such as storing the data unitin the sample entry after excluding the data unit from the sample data.

Also, information on each of the plurality of data units is stored inascending order of decryption. For example, when one access unit ofMPEG-4 AVC is stored as one PES packet, the data unit corresponds to theNAL unit, and a number of NAL units that constitute the access unit isindicated by num_of_data_unit. Then, conversion_mode is set to 1 for theNAL unit of each of SPS and PPS. Also, each of the LATM header and theLATM payload may be regarded as the data unit. In this case, thisAU_info table can be applied also to MPEG-4 AAC by settingconversion_mode to 1 for the data unit corresponding to the LATM header.When the plurality of access units is stored in the PES packet,number_of_data_unit denotes the total number of data units included inall the access units in the PES packet.

Note that the AU_info table may be stored in adaptation_field of theheader of the TS packet including a starting section of the PES packet(TS Header of FIG. 3). The AU_info table may be stored as part of thecoded data such as the NAL unit or SEI (Supplemental EnhancementInformation) in MPEG-4 AVC or HEVC. When the AU_info table is stored aspart of the coded data, the AU_info table may be stored for each accessunit or each random access. Also when the AU_info table is stored in theTS packet or PES packet, the AU_info table may be stored for each PESpacket, and the AU_info table may be stored only in the PES packetincluding the access unit that comes first in order of decryption in therandom access unit. When the AU_info table is stored for each randomaccess unit, information regarding all the access units that constitutethe random access unit is stored in the AU_info table.

FIG. 14 is a block diagram illustrating a configuration of the filegenerating apparatus according to the present variation.

File generating apparatus 100 according to the present variationconverts the transport stream including the AU_info table into an MP4file to generate the MP4 file. This file generating apparatus 100includes supplementary information search unit 101, supplementaryinformation analysis unit 103, and generation unit 104. Supplementaryinformation search unit 101 searches the transport stream for theAU_info table, which is the supplementary information. Based on a resultof the search, supplementary information analysis unit 103 determineswhether the AU_info table exists. Furthermore, on determination that theAU_info table exists, supplementary information analysis unit 103analyzes the AU_info table. Based on an analysis result made bysupplementary information analysis unit 103, generation unit 104generates the MP4 file.

Specifically, generation unit 104 includes sample generation unit 104 aand sample entry generation unit 104 b. Sample generation unit 104 astores data such as data of the LATM payload or the NAL unit other thanSPS and PPS in mdat of the MP4 file as sample data. Sample entrygeneration unit 104 b stores data such as the data of the LATM header orthe NAL unit of each of SPS and PPS in the sample entry in stsd withinmoov of the MP4 file.

Such a file generating apparatus 100 can easily convert the transportstream including the AU_info table described above into the MP4 file.

As described above, when the coded data of audio or video is to bestored, a storage place of the initialization information required fordecryption differs between MPEG2-TS and MP4. Furthermore, a storageformat of the NAL unit in MPEG-4 AVC or HEVC differs between MPEG2-TSand MP4. Therefore, conversion of the storage format is needed forconversion from the transport stream to the MP4 file. Hereinafter, thestorage format of the NAL unit in MPEG2-TS and MP4 will be describedwith reference to FIG. 15A to FIG. 15C.

FIG. 15A is a diagram illustrating schematic structure of the NAL unit.

The NAL unit includes a header and a payload. The header stores typeinformation that indicates a type of data to be stored in the payload.

FIG. 15B is a diagram illustrating an example of the storage format ofthe NAL unit in MPEG2-TS. In MPEG2-TS, in order to identify a boundaryof the NAL unit, a unique bit string called a start code is appended tothe NAL unit as identification information (hereinafter such a form ofthe identification information is referred to as a start code form). Anapparatus such as a decryption apparatus can separate a desired NAL unitby searching for the start code and the type information stored in theheader of the NAL unit.

FIG. 15C is a diagram illustrating an example of the storage format ofthe NAL unit in MP4. In MP4, in order to identify the boundary of theNAL unit, a field that indicates a data size of the NAL unit as theidentification information is appended to the NAL unit (hereinafter sucha form of the identification information is referred to as an NAL sizeform). Here, a field length of the field that indicates the data size isstored in AVCDecoderConfigurationRecord in the sample entry.AVCDecoderConfigurationRecord is a region where information such as theinitialization information for decryption is stored. An apparatus suchas a decryption apparatus can separate the desired NAL unit based on thedata size of the NAL unit.

As described above, MPEG2-TS differs from MP4 also in whether the formof the identification information indicating the boundary of the NALunit is the start code form or the NAL size form. Therefore, whenconverting the transport stream into the MP4 file, it is necessary toconvert the identification information that indicates the boundary ofthe NAL unit. Note that since the storage format of the NAL unit isspecified for each coding scheme, an operation of conversion to the MP4file may be switched with reference to the coding scheme of audio orvideo.

In conversion to the MP4 file, when data of the coding scheme of the NALsize form is handled, the data size of the NAL unit is required.Therefore, the data size of the NAL unit that constitutes the accessunit may be preferably acquired in advance. This allows an amount ofprocessing for determining the data size of the NAL unit to be reduced,by searching the access unit in the start code form for the start codeand detecting the NAL unit boundary.

That is, size information that indicates the data size of each NAL unitincluded in the access unit is stored in top of the access unit in thetransport stream according to the present variation.

FIG. 16A is a diagram illustrating an example of a configuration of theaccess unit in the transport stream according to the present variation.As illustrated in this FIG. 16A, size information that indicates thedata size of each NAL unit that constitutes the access unit multiplexedin the transport stream is stored in top of the access unit. Forexample, this size information is stored in a newly defined sizeinformation NAL unit. The types of the NAL unit include a type forprivate and a type for user data. Therefore, any type is selected fromthese types, and the selected type of the NAL unit is used as the sizeinformation NAL unit. Since the size information does not need to beencrypted, this size information NAL unit is stored in plain text.

FIG. 16B is a diagram illustrating an example of syntax of the sizeinformation included in the size information NAL unit. The sizeinformation includes number_of_nalu and nal_size. number_of_nalu denotesa number of NAL units that constitute the access unit, and nal_sizedenotes the data size of each NAL unit. Since the size information NALunit is not stored in the MP4 file, the size information does not needto indicate the data size of the size information NAL unit itself. Notethat in the example illustrated in FIG. 16A, the size information NALunit is arranged before the NAL unit for signaling top of the accessunit called Access Unit Delimiter (AUD). However, the size informationNAL unit may be arranged immediately after AUD. When the sizeinformation NAL unit is arranged immediately after AUD, the sizeinformation on the size information NAL unit indicates the size of eachNAL unit after AUD. Therefore, the size information does not indicatethe data size of AUD. However, since the data size of AUD is fixed, filegenerating apparatus 100 may store the data size in advance. Also, in asimilar manner to the AU_info table, the size information may bearranged at top of the payload of the PES packet.

FIG. 16C is a diagram illustrating another example of syntax of the sizeinformation included in the size information NAL unit.

As illustrated in FIG. 16A, in addition to the start code, avariable-length code, such as zero_byte, may be included before the NALunit in the transport stream. Therefore, as illustrated in FIG. 16C, thesize information may store a data size (prefix_size illustrated in FIG.16C) of the identification information including the start code of theNAL unit. Note that when the data size of the identification informationis fixed, the data size of the identification information may be storedin a descriptor of MPEG2-TS or in the supplementary data for conversionto the MP4 file. Furthermore, the NAL size form may also indicate thefield length of the field that indicates the data size of the NAL unitafter conversion to the MP4 file.

Also, the identification information may be regarded as a data unit, andthe AU_info table may indicate content of Nal_size_info. At this time,by making conversion_mode multiple-valued, in addition to two operationsincluding deleting and leaving the data unit, a mode for converting datastructure of the data unit may be added. Furthermore, identificationinformation for identifying a type of the data unit may be added to theAU_info table. For example, such identification information enablesdiscrimination of a type of NAL unit, such as the NAL unit of SPS inMPEG-4 AVC or HEVC, NAL unit of PPS, and NAL unit of slice.Alternatively, such identification information enables discrimination ofthe LATM header or LATM payload of MPEG-4 AAC, etc. Furthermore, a fieldthat indicates whether the data unit is encrypted may be providedseparately.

A data unit with different conversion_mode may be stored in a differentTS packet. Also, when conversion_mode is 2, the data unit to be storedin the sample entry as header information may be stored in the TS packetas plain text.

Regarding encryption, only the NAL unit of slice data may be encrypted,and other sections may be plain text. This is because encryption isperformed on a TS packet-by-TS packet basis, plain text and encryptedsection cannot be intermingled in the payload of the TS packet, the datasize of AUD is small, and storing AUD as an independent packet leads toincrease in stuffing and decrease in a multiplexing efficiency. Also,when the boundary of the encrypted NAL unit data of slice is not alignedat an end of the payload of the TS packet, stuffing is required.Stuffing may be performed by a method for using adaptation_field of theTS packet header, or a method for inserting data such as a Filler DataNAL unit or SEI for Filler Data into the coded data. Whenadaptation_field of the TS packet header is used, the adaptation_fieldneeds to be plain text, but switching processing of whether to encrypt avariable-length region imposes a high load. Therefore, when performingstuffing, it is preferable to align the boundary of the NAL unit data ata payload end of the TS packet by using data structure for stuffing inthe coded data.

Also, SEI for user data storage (User unregistered SEI) may be insertedinto Adaptation field of the TS packet or the access unit, and the sizeinformation may be stored in the SEI. In conversion into the MP4 file,the start code form can be converted into the NAL size form, based onthe size information on the NAL unit stored by one or more of thesemethods. Also, information that indicates whether the size informationis stored may be stored using information such as the descriptor inMPEG2-TS.

FIG. 17 is a flowchart illustrating a processing operation of filegenerating apparatus 100 according to the present variation generatingthe MP4 file. Specifically, this flowchart illustrates an example of theprocessing operation of converting the transport stream to the MP4 filewith reference to the AU_info table illustrated in FIG. 13C.

Supplementary information search unit 101 of file generating apparatus100 searches for the AU_info table arranged at top or the like of thepayload of the PES packet (step S101). Next, based on a result of thesearch, supplementary information analysis unit 103 determines whetherthe AU_info table exists (step S102). When it is determined here thatthe AU_info table exists (“Yes” in step S102), supplementary informationanalysis unit 103 acquires the data size of each data unit and aconversion mode of the data unit included in the AU_info table (stepS103). On the other hand, when it is determined that the AU_info tabledoes not exist (“No” in step S102), sample generation unit 104 a ofgeneration unit 104 regards the access unit separated from the PESpacket as a data unit, and copies and pastes the data unit on mdat assample data (step S105). When one access unit is stored in one PESpacket, sample generation unit 104 a regards the payload of the PESpacket as data for one access unit, and separates the payload. When aplurality of access units is stored in one PES packet, or when theaccess unit is fragmented and stored in the PES packet, samplegeneration unit 104 a searches for the boundary of each access unit inthe coded data, and separates those access units.

After step S103, supplementary information analysis unit 103 determineswhether the conversion mode is 0 (step S104). When it is determined thatthe conversion mode is 0 (“Yes” in step S104), sample generation unit104 a copies and pastes the data unit corresponding to the conversionmode on mdat as sample data (step S105). On the other hand, when it isdetermined that the conversion mode is not 0 (“No” in step S104),supplementary information analysis unit 103 determines whether theconversion mode is 1 (step S106). When it is determined here that theconversion mode is 1 (“Yes” in step S106), sample generation unit 104 aconverts data structure of the data unit corresponding to the conversionmode, and stores, in mdat, the data unit that has data structure afterconversion as sample data (step S107). For example, sample generationunit 104 a converts the form of the identification information on theNAL unit boundary from the start code form into the NAL size form. Onthe other hand, when it is determined that the conversion mode is not 1but 2 (“No” in step S106), sample entry generation unit 104 b stores atleast part of data of the data unit in the sample entry, without storingthe data unit corresponding to the conversion mode in mdat (step S108).For example, sample entry generation unit 104 b stores the NAL unit ofeach of SPS and PPS in MPEG-4 AVC in the sample entry. Alternatively,sample entry generation unit 104 b separates AudioSpecificConfig( ) fromthe LATM header of MPEG-4 AAC, and stores AudioSpecificConfig( ) in thesample entry. Of the data of the data unit, although a section to bestored in the sample entry is specified in the coding scheme in advance,supplementary data for specifying a storage section in the sample entrymay be indicated in the AU_info table.

Note that in the above-described exemplary embodiment and eachvariation, each component may be made of dedicated hardware, or may beimplemented through execution of a software program suitable for eachcomponent. Each component may be implemented by a program executionunit, such as a CPU or a processor, reading and executing the softwareprogram recorded in a recording medium, such as a hard disk or asemiconductor memory. Here, software that implements the file generatingapparatus according to the above-described exemplary embodiment and eachvariation causes a computer to execute each step included in theflowchart illustrated in FIG. 8 or FIG. 17.

Although the file generating apparatus according to one or more aspectshas been described above based on the exemplary embodiment and eachvariation, the present disclosure is not limited to this exemplaryembodiment and each variation. The exemplary embodiment and eachvariation to which various modifications conceivable by a person skilledin the art are made, and aspects that are made by combining elements ofthe exemplary embodiment and each variation may also be within the scopeof the one or more aspects as long as such aspects do not depart fromthe gist of the present disclosure.

For example, in the exemplary embodiment and each variation, a file madeby MPEG2-TS is used as the original file. However, the original filesmay be any file or transport stream other than the file of MPEG2-TS, ifthe original file is a file made in a file format different from MP4.

Also, the present disclosure may also include the following cases.

(1) Specifically, each of the above-described apparatuses is a computersystem that includes devices such as a microprocessor, a ROM, a RAM, ahard disk unit, a display unit, a keyboard, and a mouse. The RAM or harddisk unit stores a computer program. Each apparatus achieves a functionthereof by the microprocessor running in accordance with the computerprogram. Here, the computer program is constructed through combinationof a plurality of instruction codes that indicate directions to thecomputer for achieving a predetermined function.

(2) Part or all of the components that constitute each of theapparatuses may be made of one system LSI (Large Scale Integrationcircuit). The system LSI is a super-multifunctional LSI manufactured byintegration of a plurality of elements on one chip, and specifically isa computer system that includes a microprocessor, a ROM, a RAM, etc. TheRAM stores the computer program. The system LSI achieves the functionthereof by the microprocessor operating in accordance with the computerprogram.

(3) Part or all of the components that constitute each apparatusdescribed above may include an IC card or a standalone module detachablefrom each apparatus. The IC card or the module is a computer system thatincludes a microprocessor, a ROM, a RAM, etc. The IC card or the modulemay include the above-described super-multifunctional LSI. The IC cardor the module achieves the function thereof by the microprocessoroperating in accordance with the computer program. This IC card or thismodule may be tamper-proof.

(4) The present disclosure may be the method described above. Also, thepresent disclosure may be a computer program that causes a computer toimplement these methods, and may be a digital signal made of thecomputer program.

The present disclosure may be the computer program or the digital signalrecorded in a computer-readable recording medium, such as a flexibledisk, a hard disk, a CD-ROM, an MO, a DVD, a DVD-ROM, a DVD-RAM, a BD(Blu-ray (registered trademark) Disc), and a semiconductor memory, forexample. Also, the present disclosure may be the above-described digitalsignal recorded in these recording media.

Also, the present disclosure may transmit the computer program or thedigital signal via electric telecommunication lines, wireless or wiredcommunication lines, a network represented by the Internet, databroadcasting, etc.

Also, the present disclosure may be a computer system including amicroprocessor and a memory, the memory may store the computer program,and the microprocessor may operate in accordance with the computerprogram.

Also, the present disclosure may be implemented by another independentcomputer system through recording of the program or the digital signalin the recording medium and transportation, or through transportation ofthe program or the digital signal via the network or the like.

(5) The above-described exemplary embodiment and the variations may becombined with one another.

Although the data transmission method, the data playback method, etc.according to one or more aspects of the present disclosure have beendescribed above on the basis of the exemplary embodiment, the presentdisclosure is not limited to this exemplary embodiment. The presentexemplary embodiment to which various modifications conceivable by aperson skilled in the art are made, and exemplary embodiments that aremade by combining elements of different exemplary embodiments may alsobe within the scope of the one or more aspects of the present disclosureas long as such aspects do not depart from the gist of the presentdisclosure.

The present disclosure produces an effect of reducing the processingload. The present disclosure is applicable, for example, to an apparatusthat converts the file format from MPEG2-TS to MP4, and can be used fordevices such as a smart phone and a tablet, for example.

What is claimed is:
 1. A file generating method for generating an MP4file, the file generating method comprising: acquiring an original filemade in a file format different from MP4; acquiring a difference fileincluding data that is not included in the original file; acquiring aprocedure file indicating a procedure for generating the MP4 file; andgenerating the MP4 file by combining the data included in the differencefile with data included in the original file in accordance with theprocedure indicated in the procedure file, wherein in acquisition of theoriginal file, the original file in plain text is acquired, and ingeneration of the MP4 file, every time a section that constitutes theoriginal file is acquired, a portion of the MP4 file corresponding tothe section is generated and encrypted, and every time the portion thatconstitutes the MP4 file is encrypted, the section of the original filecorresponding to the portion is deleted.
 2. The file generating methodaccording to claim 1, wherein in acquisition of the original file, theoriginal file made in a file format of MPEG2-TS is acquired.
 3. The filegenerating method according to claim 1, wherein in acquisition of theoriginal file, the difference file, and the procedure file, acquisitionis performed through reading of the original file, the difference file,and the procedure file from an optical disc.
 4. The file generatingmethod according to claim 1, wherein the procedure file describes rangesof a plurality of respective sections included in the difference file,and ranges of a plurality of respective sections included in theoriginal file, so that the ranges of the sections included in thedifference file and the ranges of the sections included in the originalfile are arranged alternately, and in generation of the MP4 file, theMP4 file is generated through combination of the sections indicated bythe respective ranges in order of the respective ranges described in theprocedure file.
 5. The file generating method according to claim 4,wherein the ranges of the plurality of respective sections included inthe difference file are described in the procedure file in data size,and the ranges of the plurality of respective sections included in theoriginal file are described in the procedure file in starting positionand data size of the sections.
 6. The file generating method accordingto claim 1, wherein the data size of the MP4 file is described in theprocedure file, and the file generating method further comprisesdetermining whether a medium has free space for recording the MP4 filebased on the data size of the MP4 file described in the procedure file.7. The file generating method according to claim 1, wherein an attributeof the MP4 file is described in the procedure file, and the filegenerating method further comprises reading the attribute described inthe procedure file.
 8. The file generating method according to claim 1,wherein a buffer size required for playback of the MP4 file is describedin the procedure file, and the file generating method further comprisesreading the buffer size described in the procedure file.
 9. The filegenerating method according to claim 1, wherein a first file name, whichis a name of the original file, and a second file name, which is a nameof the difference file, are described in the procedure file, and thefile generating method further comprises specifying a file with thefirst file name described in the procedure file as the original file,and specifying a file with the second file name described in theprocedure file as the difference file.
 10. The file generating methodaccording to claim 1, wherein in generation of the MP4 file,MP4-conforming header information that is data included in thedifference file is combined with data included in the original file. 11.A file generating apparatus for generating an MP4 file, the filegenerating apparatus comprising: an original file acquisition unit thatacquires an original file made in a file format different from MP4; adifference file acquisition unit that acquires a difference fileincluding data that is not included in the original file; a procedurefile acquisition unit that acquires a procedure file indicating aprocedure for generating the MP4 file; and a generation unit thatgenerates the MP4 file by combining the data included in the differencefile with data included in the original file in accordance with theprocedure indicated in the procedure file, wherein in acquisition of theoriginal file, the original file in plain text is acquired, and ingeneration of the MP4 file, every time a section that constitutes theoriginal file is acquired, a portion of the MP4 file corresponding tothe section is generated and encrypted, and every time the portion thatconstitutes the MP4 file is encrypted, the section of the original filecorresponding to the portion is deleted.